WLANs (Wireless Local Area Networks) utilize RF (Radio Frequency) signals or light signals to connect mobile endpoints to each other or to a centralized gateway and transmit data over a wireless medium between the physical endpoints or between a mobile endpoint and an endpoint on a network that is connected to the WLAN. In 1997 the IEEE published standards for WLANs under the title of 802.11 (also known as “Wi-Fi”). The IEEE 802.11b protocol has gained popularity over the past few years and deployment of 802.11b networks is expected to increase significantly in the near future. Currently, most of these networks are used for data access from laptop computers and personal digital assistants (PDAs). The basic hardware setup of an IEEE 802.11 network is the Basic Service Set (BSS), which is merely a number of endpoint stations that communicate with one another. And ESS is larger than a BSS and can be a combination of BSSs or a BSS and other associated network nodes, components, and LAN lines. Using a WLAN to place voice phone calls using VoIP (Voice over Internet Protocols) over WLAN is also expected to grow significantly in the near future. However, VoIP over WLAN presents a unique set of problems that must be addressed prior implementing this technology.
There exists a plurality of 802.11 standards that each use different frequency bands and have varying data transmission speeds. The original IEEE 802.11 standard supported wireless interfaces operating at speeds of up to 2 megabyte per second (Mbps) in the 2.4 GHz radio band. By using different modulation techniques, IEEE 802.11b raised the data transmission rates to 11 Mbps, while 802.11a supports up to 54 Mbps transmission rates at a 5 GHz frequency. The IEEE 802.11g is developing a standard for data transmission rates of 54 Mbps at the 2.4 GHz frequency.
WLANs under 802.11 use media access control (MAC) protocols to transmit between wired and wireless devices. Each wireless network card is assigned a MAC address used to identify the station. In a BSS, IEEE 802.11 enables wireless mobile stations (STAs) to communicate through a wireless network interface directly with each other or with other stations through an access point. An access point (AP) is a centralized gateway providing message and power management and access to an external LAN (Local Area Network) and/or the Internet.
The access to wireless networks is controlled by coordination functions. The distributed coordination function (DCF) provides access similar to Ethernet CSMA/CA access. The DCF determines if the RF link between devices is clear prior to transmitting. Stations use a random backoff after every frame to avoid collisions. Endpoint stations provide MAC Service Data Units (MSDUs) after detecting no current transmissions. The MSDUs functions to transmit data frames to the proper endpoint station.
FIG. 1 illustrates a schematic diagram of an exemplary WLAN enterprise network under IEEE 802.11 protocols. One basic service set (BSS) has a wireless access point (AP1) 12 and a second BSS has a wireless access point (AP2) 14. An AP bridges data with wireless STAs that are associated with that AP. An enterprise network typically has multiple BSSs and multiple APs distributed throughout an office complex or among floors on buildings so that a STA may be operated from nearly anywhere in a complex or building. Each AP in a BSS has an RF propagation broadcast area that has an effective range based upon broadcast power, natural signal attenuation, and interferences. AP1 12 has an RF propagation area defined exemplarily by coverage ring 13, and AP2 14 has an RF propagation area defined exemplarily by coverage ring 15. A WLAN may also be used to send voice data signals using a WIPP (Wireless Internet Protocol Phone or IP Phone) 16 that transmits data signals using voice protocols, such as voice over Internet Protocol (VoIP). Notebook computer 18 is associated with AP1 12 using a wireless network interface card and transmits data using IEEE 802.11 protocols. Both APs 12,14 are connected to an internal corporate Intranet 20. The Internet 26 may be accessed through intranet 20 and gateway 22 or alternatively through AP1 12 through a Radius authentication server 24.
The first steps in improving WLAN performance is to identify the network the STA is operating in and to determine the current network status in terms of congestion, interference and cell overlap. It is rare of APs to inform the nodes about the congestion level in the BSS. If the STA is working with an AP which supplies no network status information, it is up to the STA to determine the current congestion level of the network. A starting point is to define network congestion. A BSS is congested if the traffic generated by all STAs present in the BSS is high enough to cause significant packet loss.
Packet loss is usually a good indicator of the network status. However, packet loss in the wireless network can occur due to many reasons: congestion from other 802.11 nodes in the BSS, being far away from the AP, or due to interference with cordless phones, Bluetooth® signals, or microwaves signals, since 802.11 operates in the license-free frequency range of 2.4 GHz. A problem with prior art methods is the inability to determine reasons for packet loss.